1. Field of the Invention
The present invention relates to a communication apparatus and a portable telephone.
2. Description of the Related Art
In recent years, guidelines on local absorption covering communication apparatuses and portable telephones have been established in many countries. As the quantity for evaluation of local absorption, for example, there is the SAR (specific absorption rate) indicating the power of the electromagnetic energy absorbed per unit mass. For example, the Japanese guidelines on local absorption stipulate that the peak value of the average SAR for 10 g of tissue not exceed 2W/kg.
In “Decrease of Local SAR and Ensuring of Communication Characteristics by Control of Current at Surface of Housing of Portable Telephone” (Journal of Magnetics Society of Japan, Vol. 23, No. 10, pp. 2005-2008, (1999)), it is described to decrease the local SAR by attaching a ferrite sheet to a metal housing of a portable telephone.
The SAR has a tendency of becoming higher the larger the transmitting output of the communication apparatus and portable telephone and of becoming higher the closer the distance between the source of the electric wave of the communication apparatus and portable telephone and the human body.
In a portable telephone, the position where the SAR (local SAR) becomes the highest sometimes becomes a portion other than the antenna, for example, the vicinity of the shield case. This is derived from the fact that the shield case acts as part of the antenna and that the shield case is brought closer to the human head than the antenna at the time of a call.
In such case, the SAR can be decreased by attaching an electric wave absorber to the shield case of the portable telephone, more concretely, by attaching a sheet-type electric wave absorber on the human head side of the shield case by using an insulating adhesive, however, it is desirable to further decrease the SAR.